[PATCH 5.7 313/376] iommu/vt-d: Only clear real DMA devices context entries

[Greg Kroah-Hartman]

From: Jon Derrick <jonathan.derrick@xxxxxxxxx>

commit 8038bdb8553313ad53bfcffcf8294dd0ab44618f upstream.

Domain context mapping can encounter issues with sub-devices of a real
DMA device. A sub-device cannot have a valid context entry due to it
potentially aliasing another device's 16-bit ID. It's expected that
sub-devices of the real DMA device uses the real DMA device's requester
when context mapping.

This is an issue when a sub-device is removed where the context entry is
cleared for all aliases. Other sub-devices are still valid, resulting in
those sub-devices being stranded without valid context entries.

The correct approach is to use the real DMA device when programming the
context entries. The insertion path is correct because device_to_iommu()
will return the bus and devfn of the real DMA device. The removal path
needs to only operate on the real DMA device, otherwise the entire
context entry would be cleared for all sub-devices of the real DMA
device.

This patch also adds a helper to determine if a struct device is a
sub-device of a real DMA device.

Fixes: 2b0140c69637e ("iommu/vt-d: Use pci_real_dma_dev() for mapping")
Cc: stable@xxxxxxxxxxxxxxx # v5.6+
Signed-off-by: Jon Derrick <jonathan.derrick@xxxxxxxxx>
Acked-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200527165617.297470-2-jonathan.derrick@xxxxxxxxx
Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/iommu/intel-iommu.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -2582,6 +2582,12 @@ static int domain_setup_first_level(stru
 					     flags);
 }
 
+static bool dev_is_real_dma_subdevice(struct device *dev)
+{
+	return dev && dev_is_pci(dev) &&
+	       pci_real_dma_dev(to_pci_dev(dev)) != to_pci_dev(dev);
+}
+
 static struct dmar_domain *dmar_insert_one_dev_info(struct intel_iommu *iommu,
 						    int bus, int devfn,
 						    struct device *dev,
@@ -5286,7 +5292,8 @@ static void __dmar_remove_one_dev_info(s
 					PASID_RID2PASID);
 
 		iommu_disable_dev_iotlb(info);
-		domain_context_clear(iommu, info->dev);
+		if (!dev_is_real_dma_subdevice(info->dev))
+			domain_context_clear(iommu, info->dev);
 		intel_pasid_free_table(info->dev);
 	}